Do you really wish anybody to break a leg? Of course not! You want them to stay healthy—especially if one of your kids is just going to have a theater debut.
So where does this exclamation, “Break a leg!” come from? Why say it when you wish someone all the possible success in the world?
The etymology of “break a bone” is correctly derived from the German “Hals- und Beinbruch!” (“neck and leg fracture”). After WWI and well into the 1930s, before “curtain up,” Jewish actors would whisper to each other “mazel we-brokheh!” (“fortune and blessings!”), the Yiddish common phrase under such circumstances.
Then remember, at that period of time in Germany, it started to—and then was—life threatening to be recognized as a Jew.
Coincidently, of course they were overheard. So the ruse was to say that they wished “Hals- und Beinbruch” to each other, only just to avoid such a thing to happen at all.
To really appreciate the connection between the German and Yiddish phrases, you need to be able to hear it. Perhaps you find a person in your vicinity who speaks both languages who can demonstrate it for you.
So “break a leg!” (And stay healthy!)